The present invention relates to a method of manufacturing a metal container.
Heretofore, a container known as a three-piece can comprising a bottom, a cover and a body has been widely used for preservation of foodstuff. The three-piece can is constructed by bending a flat sheet into a cylindrical shape with the seam adhered or welded together to make the body and then curling the bottom and the cover tight to fasten them to the body.
A metal container was proposed which is manufactured firstly by drawing and ironing a thin sheet material into a cup-shaped can having a body integral with a bottom and then curling a cover tight to fasten it to the can. Compared with the three-piece can, this can is called a two-piece can from the number of components and also called a DI can from the drawing and ironing process. Since it is possible to iron the body wall thin and make the container lightweight, the DI can can economize on consumption of the material. The DI can is simple in its manufacturing process and has a good productivity so that it can be mass-produced to meet a great demand. Further, the DI can causes little leakage and has a good appearance. Consequently, the DI can has rapidly come into wide use as a container for carbonated drink and beverage having a high internal pressure, such as beer and soda, or as an aerosol container for cosmetics.
In contrast to the three-piece can which has its seam exposed on the cylindrical body made of a flat sheet bent and joined together, the two-piece can is advantageous in that it is seamless and has a good display effect, thus being particularly suitable for a container of cosmetics required to have a beautiful appearance.
Since the conventional DI can is of a construction where the body is integral with the bottom and the cover is curled tight to fasten it to the body, the tight curl of the cover is exposed at the shoulder of the container, worsening the appearance. Accordingly, there was proposed a reversed DI can wherein the body is integral with the cover and the bottom is fitted in the body and curled tight to fasten it to the body. In such a can construction having the cover and the body integral with each other, no curl is formed at the shoulder of the container so that a metal container having a better appearance than the conventional DI can can be obtained. Even such a container, however, exposes a curl for fastening the body to the container bottom. Therefore, it still remains unpleasing to the eye.
Accordingly, an object of the present invention is to provide a method of manufacturing a metal container which appears to have a mono block construction formed of a one-piece member, without exposing outside the tight curl for fastening the bottom to the body.
Another object of the present invention is to provide the above method of manufacturing a metal container which has a good seal at the joint between the bottom plate and the body.
A further object of the present invention is to provide a method of manufacturing a metal container which heightens its pressure-resisting strength at the bottom by improving the structure of the bottom plate.
Still a further object of the present invention is to provide a method of manufacturing the above metal container which prevents the occurrence of an explosion accident when the container is heated in a sealed condition by mistake, by using a synthetic resin material for the bottom plate.
Still a further object of the present invention is to provide a method of manufacturing the above metal container which can exert a self-sealing performance in case the bottom plate is made of a synthetic resin.
Still a further object of the present invention is to provide a method of manufacturing the above metal container which has an easily openable cover.
Still a further object of the present invention is to provide a method of manufacturing the metal container which permits application of a spray valve of a small diameter less than one inch, so as to reduce cost and make it pleasing to the eye.
Other objects and advantages of the present invention will be apparent from the following description.